The present invention relates to disk drives. More particularly, it relates to a method of reducing or removing asperities on a disk surface of a disk drive.
A magnetic disk drive apparatus is an apparatus for recording and reading data on the surfaces of spinning disks through the use of a changing magnetic field. One or more data storage disks are coaxially mounted on a hub of a spindle motor. The spindle motor rotates the disks at speeds typically on the order of several thousand to tens of thousands of revolutions-per-minute. Digital information, representing various types of data, is typically written to and read from the data storage disks by one or more transducers, or read/write heads, which are mounted to an actuator assembly and hover above the surface of the rapidly rotating disks.
The transducer head is typically in the form of a magnetoresistive (MR) head or element carried on a slider body. Oftentimes, the slider and transducer are designated as a xe2x80x9cheadxe2x80x9d. Regardless, the slider body is mounted to a flexible suspension portion of an arm assembly that is otherwise part of the actuator assembly. Further, the slider includes one or more pads that generate an air bearing upon rotation of the disk. More particularly, the slider is positioned by the actuator assembly over a surface of a disk. As the disk rotates, an air bearing develops between the slider and the disk surface, causing the slider, and thus the read/write head, to lift and fly several micro inches above the disk surface. The distance between the slider and the disk surface is often times referred to as a xe2x80x9cfly heightxe2x80x9d. In magnetic recording technology, it is desired to xe2x80x9cflyxe2x80x9d the slider as closely as possible to the disk surface (i.e., minimal fly height) so that the read transducer can distinguish between the magnetic fields emanating from closely spaced regions on the disk.
A common problem encountered during operation of a disk drive is the presence of one or more asperities on the relevant disk surface. In basic terms, an asperity is an unexpected projection formed on the otherwise planar disk surface. In operation, the MR element may physically contact the asperity due to the minuscule fly height. Contact between MR element and asperity can prevent reading and/or writing of data onto the disk at the particular track location of the asperity. Further, depending upon the form of the asperity and the number of contacts, the MR element itself can be damaged.
Due to their highly undesirable effects, every effort is made during disk manufacture to eliminate asperities. However, it is virtually impossible to prevent asperity formation. Further, asperities are often created post-manufacture. That is to say, during normal operation of the disk drive following assembly (or xe2x80x9coperational disk drivexe2x80x9d), certain events may occur causing a particle to deposit or wedge itself onto the disk surface, resulting in a deleterious asperity. Thus, it is highly desirable to provide an operational disk drive with the ability to reduce or xe2x80x9cburnishxe2x80x9d asperities during use.
Because the fly height will decrease with a reduction in disk speed (or rate of rotation), the most common technique for burnishing asperities is to simply reduce the disk speed. The slider is then positioned over the asperity location, and allowed to repeatedly contact and burnish the asperity with continued disk rotation. In fact, this same technique is employed during disk manufacture, except that the slider does not include an MR element that would otherwise be potentially damaged by the repeated contacts. Unfortunately, this technique is of limited applicability with more recently available disk drives configured to provide a negative air bearing. With a negative air bearing, the fly height remains virtually unchanged with the relatively small reductions in disk speed, otherwise utilized for asperity burnishment. Instead, the disk sped must be greatly reduced, to a point where the fly height is no longer stable. Further, at these low disk speeds, contact between the slider and the asperity is likely insufficient to burnish the asperity, as described below. As a result, the disk speed reduction technique for burnishing asperities is ineffective with operational disk drives utilitizing negative pressure air bearings.
A related concern associated with accepted asperity burnishing techniques, regardless of the type of air bearing employed, is that the kinetic energy generated upon contact between slider and asperity is inherently lowered with a reduction in disk speed. Obviously, the burnishing effect is diminished with lower kinetic energy. This relationship is especially problematic for negative air bearing designs where the disk speed must be dramatically reduced to provide an appropriate fly height. With this in mind, a more effective burnishing technique for an operational disk drive would entail an increase in disk speed relative to normal operational conditions. Unfortunately, the fly height becomes larger with an increase in disk speed. As such, simply increasing disk speed is not a viable burnishing technique for an operational disk drive.
Detrimental disk surface asperities are frequently encountered during operation of an assembled disk drive. Unfortunately, the accepted burnishing technique of lowering disk speed to reduce fly height is no longer applicable to current disk drive systems in which a negative pressure air bearing is formed, and is inefficient from a kinetic energy standpoint. Therefore, a need exists for a system and method of burnishing asperities with an operational disk drive with increased disk speed.
One aspect of the present invention provides a method of burnishing an asperity on a magnetic surface of an operational disk drive. The disk drive includes a slider including a pad and an MR element. Rotation of the disk relative to the slider forms an air bearing between the slider and the disk surface, the air bearing generating a fly height of the MR element relative to the disk surface. With this in mind, the method includes identifying the presence of the asperity. The disk speed is increased from a normal operational rate to a first burnishing rate. Further, an internal pressure of the disk drive is reduced from a normal operational pressure to a first burnishing pressure. A first burnishing fly height is thusly established at the first burnishing rate and the first burnishing pressure. In this regard, the first burnishing fly height is less than a fly height otherwise found with the disk drive operating at the first burnishing rate and the normal operational pressure. The slider is then positioned over the asperity. Finally, the asperity is contacted by the slider upon continued rotation of the disk at the first burnishing fly height, thereby burnishing the asperity. In one preferred embodiment, the method further includes determining whether the asperity remains after operating the disk drive at the first burnishing rate and the first burnishing pressure following a certain time period. If the asperity has not been sufficiently reduced, the disk speed is increased to a second burnishing rate and the internal pressure is reduced to a second burnishing pressure resulting in a second burnishing fly height. Once again, the second burnishing fly height is less than a fly height than would otherwise be found with the disk drive operating at the second burnishing rate and normal operational pressure. With resulting contact between the slider and the asperity at the second burnishing rate, the asperity is further burnished.
Another aspect of the present invention relates to a system for controlling operation of an operational disk drive. The disk drive includes a slider maintaining a pad and an MR element, and a magnetic disk rotated by a spindle motor. With this in mind, the system includes an asperity identifier, a spindle motor controller, an internal pressure controller, and an actuator motor controller. The asperity identifier is capable of detecting the presence of an asperity on a surface of the disk. The spindle motor controller is capable of increasing a speed of the disk from a normal operational rate to a first burnishing rate upon detection of an asperity by the asperity identifier. The internal pressure controller is capable of reducing an internal pressure of the disk drive from a normal operational pressure to a first burnishing pressure upon detection of an asperity by the asperity identifier. In this regard, the spindle motor controller and the internal pressure controller operate in concert to provide a first burnishing fly height of the slider relative to the disk surface. The first burnishing fly height is less than a fly height otherwise generated when the disk drive is operated at the first burnishing rate and the normal operational pressure. Finally, the actuator motor controller is capable of positioning the slider over the asperity at the first burnishing fly height to burnish the asperity. In one preferred embodiment, the system further includes a processor capable of prompting operation of the spindle motor controller and the internal pressure controller in accordance with a predetermined fly height correlation between disk rate and internal pressure.